This invention relates to acoustic ink printing and, more particularly to, a method and apparatus which allows for cleaning and maintaining AIP printheads which implement unique orifice plates.
It has been shown that acoustic ink printers which have printheads comprising acoustically illuminated spherical or Fresnel focusing lenses can print precisely positioned picture elements (pixels) at resolutions that are sufficient for high quality printing of complex images. Significant effort has gone into developing acoustic ink printing, see for example, U.S. Pat. Nos. 4,308,547; 4,751,530; 4,697,195; 4,751,530; 4,751,534; 5,028,937; and 5,041,849, all of which are among many commonly assigned to the present assignee.
Although acoustic lens-type droplet emitters currently are favored, there are other types of droplet emitters which may be utilized for acoustic ink printing, including (1) piezoelectric shell transducers, such as described in Lovelady et al., U.S. Pat. No. 4,308,547, and (2) interdigitated transducers (IDTs), such as described in commonly assigned U.S. Pat. No. 4,697,195. Furthermore, acoustic ink printing technology is compatible with various printhead configurations; including (1) singe emitter embodiments for raster scan printing, (2) matrix configured arrays for matrix printing, and (3) several different types of page and width arrays, arranging from (i) single row sparse arrays for hybrid forms of parallel/serial printing, (ii) multiple row staggered arrays with individual emitters for each of the pixel positions or addresses within a page width address field (i.e., single emitter/pixel/line) for ordinary line printing.
For performing acoustic ink printing with any of the aforementioned droplet emitters, each of the emitters launches a converging acoustic beam into a pool of ink, with the angular convergence of the beam being selected so that it comes to focus at or near the free surface (i.e., the liquid/air interface) of the pool. Moreover, controls are provided for modulating the radiation pressure which each beam exerts against the free surface of the ink. That permits the radiation pressure from each beam to make brief, controlled excursions to a sufficiently high pressure level to overcome the restraining force of surface tension, whereby individual droplets of ink are emitted from the free surface of the ink on command, with sufficient velocity to deposit them on a nearby recording medium.
A main attraction of acoustic ink printing is the ability to control droplet size based on the frequency of the signal provided, rather than providing on the size of the nozzle emitting the droplet. For example, an AIP printer may emit droplets magnitude in size smaller than the AIP openings. On the other hand, conventional ink jet printing requires a minimization of the nozzle itself to obtain small droplets.
While this is a benefit of AIP type printing, the size of the droplet ejectors used in acoustic ink printing are nevertheless very small. In consideration of this, maintaining the droplet ejectors in a clean state is an extremely important aspect of proper operation. Not only can dirt particles and dust (particularly paper dust) clog the ejector ports, but ejected ink droplets which do not adhere to the recording medium or have such low velocity that they return back to the orifice plate, and can build up enough to disrupt the printing process. Additionally, whereas many conventional ink jet printers require the replacement of the printheads after a somewhat short period of time, AIP printheads can have an indefinite life span. As part of extending this useful life, maintaining the printheads clean is an important aspect.
Existing examples of printhead cleaning are substantially directed to cleaning of printheads configured using the previously mentioned nozzles.
U.S. Pat. No. 4,340,897 discloses a cleaning device for an ink-jet writing head wherein the nozzles of the writing head are urged into contact with a manifold having a set of brushes thereon. Vacuum is applied through the brushes to remove excess ink from the nozzles.
U.S. Pat. No. 4,546,363 discloses a nozzle cleaning device which blows a cleaning solvent against the nozzle portion of a printer head in an ink-jet printer. The ejecting unit includes a plurality of orifices, and a quantity of cleaning solvent is sprayed, by means of a piston, onto the nozzle of the printer head.
U.S. Pat. No. 4,567,494 discloses an ink-jet printer, the nozzles of which are primed and cleaned after each print line by engaging the nozzles with an elastomeric suction cup. The suction cup includes an inner cup of foam which wipes of any residual ink droplets. The cup is connected to a vacuum pump for drawing ink out of the nozzles.
U.S. Pat. No. 4,746,938 discloses an ink-jet printer having a heat washing unit disposed beyond one end of the printing area. The heat washing unit includes an ink mist suction unit which sucks ink mist around the ink-jet unit and the anti-clogging unit, which prevents clogging of the nozzles.
U.S. Pat. No. 4,814,794 discloses a cleaning device for the nozzle of an ink-jet printer, wherein cleaning liquid is supplied from a bag in a disposable cartridge and sprayed on the side of a nozzle in the printhead.
U.S. Pat. No. 4,829,318 discloses a maintenance system for purging and cleaning an ink-jet printhead, including a self-aligning purge nozzle which floats into positive engagement with a vent hole of the printhead, and a wiping roller about which a tape of wiping cloth passes.
U.S. Pat. No. 4,853,717 discloses a maintenance station for an ink-jet printer comprising a pump for priming the printhead, and wiping means for cleaning the printhead. The wiper is stationary relative to the apparatus, so that when the printhead on a carriage passes across the wiper in the carriage motion, the wiper is moved across the front face of the printhead.
U.S. Pat. No. 5,027,134 discloses the use of a wiper blade for cleaning conventional nozzle type ink jet printheads.
U.S. Pat. No. 5,084,712 discloses a maintenance system for an ink jet printer, including a solvent supply system for spraying solvent on the faces of the ink-jets and in the ink-jet openings, and a brush for scrubbing the ink-jet faces during and immediately after the spraying process. The solvent vapors enter the jets and deprime the jets so that the ink remaining in the jets drains out back into an ink reservoir.
U.S. Pat. No. 5,184,147 discloses an ink-jet printhead maintenance system having means for applying a vacuum to the ink-jet nozzles in the printhead. An elongated wiper engages and wipes the surface of the nozzles and is preferably moved at an extremely slow rate across the surface to enhance the wiping operation. A specialized drip edge is positioned beneath the orifice surface for directing drops of ink away from the ink-jet printhead which are generated during the cleaning procedure.
U.S. Pat. No. 5,644,347 discloses the use of a wiper blade for cleaning conventional nozzle type ink jet printheads.
U.S. Pat. No. 5,793,390 discloses a maintenance device using a wicking member for applying a cleaning liquid to nozzle openings.
As previously mentioned, an ink jet printhead configuration is significantly different from the printhead of an acoustic ink printer. Therefore, attempting to use a wiper blade cleaning device or other cleaning method or apparatus designed for nozzle type printheads will not achieve desired results. For example, use of a wiper blade cleaning devices with acoustic ink printheads may result in clogging of the printhead rather than accomplishing the desired cleaning.
It has also been suggested that a non-wiping technique for improving the cleanliness of exposed surfaces of droplet ejectors for a fixed printhead would be beneficial, as described in U.S. Pat. No. 5,287,126, commonly assigned hereto. However, while such a technique has benefits, it is less desirable for moving printheads and also involves significant engineering considerations and is more specifically designed to a fixed printhead situation.
Therefore, it has been determined desirable to find a method and apparatus of cleaning/maintaining acoustic ink printheads which have unique orifice plate design in which the ink menisci are maintained at an entrance edge of the orifice plate, defined by a very thin lip.
In accordance with the present invention, there is provided a method and apparatus for providing in combination or individually a flooding, dry and wet wiping of acoustic ink printheads for maintaining the cleanliness of the exposed surfaces of the printhead. A flooding procedure initially attempts to use a printheads own ink in the cleaning process. Following the flooding operation ink on the outside surface of the orifice plate is removed by use of wiping over it with a compliant wiper blade. Next, ink inside the orifice bore is removed using a wiping station in two separate steps. The wiping station of the present invention consists of a mechanism that allows clean, absorbent material to be positioned over the orifices before each wipe.
During a first step of the wiping station operation, the absorbent material is pushed lightly over the orifices with a soft/compliant roller while the printhead is moved and the printhead is held at a certain pressure. The dirty ink, because of higher pressure inside the printhead, is unable to reenter the printhead and is absorbed by the absorbent material. In a following step, pressure inside the printhead is decreased to enable the menisci to retreat inside the lip. When the orifice is again wiped with the absorbent material, the absorbent material is pushed with more force into the orifice using the compliant roller behind it. This enables the remaining ink to be removed from the bore of each orifice as well as from the exit surface of the submerged lip, due to absorption into the absorbent material. Subsequent to the second step wiping/cleaning method the pressure inside the printhead is increased/reset to the normal operating level to enable printing resumption.
In accordance with another aspect of the present invention, the apparatus for cleaning/maintaining AIP printheads is applicable for use with inks that when dried cannot be rinsed-away/refreshed (i.e. the wetting angle between the orifice lip and ink is significantly reduced and cannot be restored close to original) ink itself. In this embodiment, a previously supplied flooding step is augmented by a step of applying a cleaning material. In this step, the clean absorbent material has a substance applied. This absorbent material with the cleaning substance is then pressed into the orifice while the printhead moves across. Finally, the orifice plate is wiped clean again with a clean dry wipe cloth. The cleaning substance is of the type that can redissolve the dried ink such that removal of the cleaning substance restores the wetting/contact angle between the orifice lip surface and the ink.